JP4693932B1 - Cylindrical silicon crystal manufacturing method and cylindrical silicon crystal manufactured by the manufacturing method - Google Patents

Abstract

The present invention provides a cylindrical silicon crystal manufacturing method and a cylindrical silicon crystal manufactured by the manufacturing method, which can manufacture a cylindrical silicon crystal from a silicon raw material without cutting.
A melt storage container made of a material having a smaller thermal expansion coefficient and higher melting point than that of silicon and a core made of a material having a larger thermal expansion coefficient and higher melting point than that of silicon are used. Silicon nitride (Si ₃ N ₄ ) is applied to the inner surface of the melt storage container and the outer surface of the core, and the core is placed inside the melt storage container. Then, the gap formed by the inner surface of the melt storage container and the outer surface of the core is filled with the silicon melt, and the bottom side of the melt storage container is maintained while maintaining the liquid-liquidity of the silicon melt. A temperature gradient is provided from the top to the top to solidify the silicon melt.
[Selection] Figure 1

Description

  The present invention relates to a cylindrical silicon crystal manufacturing method and a cylindrical silicon crystal manufactured by the manufacturing method, which makes it possible to manufacture a cylindrical silicon crystal from a silicon raw material without cutting.

  Silicon crystals used as materials for solar cells and the like are manufactured as a lump (ingot) of a predetermined size from a melt of silicon raw material. Then, these ingots are subjected to processing such as cutting and cutting so as to have a desired shape necessary for manufacturing products such as solar cells and substrates. However, when a desired shape is formed by processing an ingot, the processing takes time and energy, and the waste of the raw material generated by cutting or cutting is difficult to reuse as raw material and must be discarded. There is a problem of causing a great loss of time, energy and resources. Therefore, a method has been proposed to reduce these losses.

  As such a method, for example, Japanese Patent Laid-Open No. 4-292494 discloses a method for manufacturing a shaped crystal capable of mass-producing a high-quality silicon crystal having a desired shape. Japanese Patent Application Laid-Open No. 2002-29882 discloses a crystal manufacturing method capable of mass-producing silicon crystals having a free surface (an outer surface of a crystal body that is not bound by an external melt holding container or the like). Furthermore, JP 2008-143754 A discloses a manufacturing method in which the silicon raw material is directly made into a spherical silicon single crystal and the yield is greatly improved.

JP-A-4-292494 JP 2002-29882 A JP 2008-143754 A

  However, even the above-described conventional manufacturing methods have shapes that cannot be directly manufactured from silicon raw materials, and examples of such shapes include cylindrical bodies.

  Cylindrical silicon crystal is necessary for manufacturing a focus ring used when plasma etching a silicon wafer, for example, and is also suitable as a sputtering target for silicon. The ingot is manufactured, and the inside of the ingot is cut out in the length direction. As described above, this hollow cutting has a problem that causes a great loss of time, energy, and resources. In addition, when the bottom shape of the ingot is not a circle but a polygon, it is necessary to cut the outer periphery into a circle, resulting in further loss of time, energy, and resources. is there.

  Therefore, the present invention provides a cylindrical silicon crystal manufacturing method and a cylindrical silicon crystal manufactured by the manufacturing method, which can manufacture a cylindrical silicon crystal from a silicon raw material without cutting. The purpose is to do.

In the cylindrical silicon crystal production method according to the present invention, a melt storage container formed of a material having a smaller thermal expansion coefficient than that of the silicon crystal and a higher melting point, and a larger thermal expansion coefficient than that of the silicon crystal, Use a core made of high material. Silicon nitride (Si ₃ N ₄ ) is applied to the inner surface of the melt storage container and the outer surface of the core, and the core is placed inside the melt storage container. Then, the gap formed by the inner surface of the melt storage container and the outer surface of the core is filled with the silicon melt, and the bottom side of the melt storage container is maintained while maintaining the liquid-liquidity of the silicon melt. A temperature gradient is provided from the top to the top to solidify the silicon melt.

  In the present invention, the liquid-repellent property is the same as defined in Patent Documents 1 to 3, and means that the high-temperature material melt is in a “non-wetting state” on the surface of the substrate or container that supports it. . “Wet” refers to the interaction between the liquid and the surface of the solid, and means that the liquid placed on the surface of the solid spreads uniformly on the surface of the solid. , Balls and spheres. The state in which water is not wet is said to be "water repellency", but this term is for liquids near room temperature, whereas liquidity is universal for "no wettability" in a wider temperature range. Expressive.

  In addition, the liquid spillability of the silicon melt is that silicon nitride is applied to the inner surface of the melt storage container and the outer surface of the core, and the core is made of a predetermined ceramic material. It can be maintained by reducing impurities such as moisture and oxygen in the surrounding environment.

The material of the melt storage container and the core may be selected in consideration of the thermal expansion coefficient (5 × 10 ⁻⁶ [/ ° C.]) of the silicon crystal, but the material of the melt storage container is silicon. Quartz (thermal expansion coefficient 5.5 × 10 ⁻⁷ [/ ° C.]) or carbon, for example, EG-20 (manufactured by Shin Nippon Techno Carbon Co., Ltd.) (thermal expansion coefficient 1.5 × 10 ⁻⁶ [/ ° C.]) and G159 (thermal expansion coefficient 0.7 × 10 ⁻⁶ [/ ° C.]) manufactured by Tokai Carbon Co., Ltd. are preferable, and the core material is silicon carbide (SiC), alumina (Al Either ₂ O ₃ ) or magnesia (MgO) is preferred.

  In the method for producing a cylindrical silicon crystal according to the present invention, the silicon crystal is made such that the purity of silicon nitride applied to the inner surface of the melt storage container and the outer surface of the core is higher than the purity of the material of the core. It is preferable to reduce impurity contamination of the body. In the present invention, purity means the ratio of main components. Therefore, the higher the purity, the smaller the content of impurities other than silicon nitride.

  The core may be held in a state where the bottom surface of the core is separated from the bottom surface of the melt storage container.

  The cylindrical silicon crystal according to the present invention is composed of columnar crystal silicon having a peripheral wall and a bottom wall that are integrally formed and having a hollow portion that opens on one side of the bottom surface and extends parallel to the axis in the longitudinal direction.

The cylindrical silicon crystal, which is the manufacturing object in the cylindrical silicon crystal manufacturing method according to the present invention, is obtained by solidifying the melt into a crystal and then lowering the temperature from the melting point (1414 ° C.) to room temperature. . However, the cylindrical silicon crystal inside the melt storage container undergoes thermal shrinkage in accordance with its thermal expansion coefficient (5 × 10 ⁻⁶ [/ ° C.) during this temperature lowering process. For example, when a cylindrical silicon crystal having an outer diameter of 100 mm and an inner diameter of 80 mm falls from 1414 ° C. to 24 ° C., the outer diameter is ΔL = 0.695 [mm] as shown in the following formula (1). There is heat shrinkage in the direction.

Here, when quartz glass having a thermal expansion coefficient of 5.5 × 10 ⁻⁷ [/ ° C.] is used for the melt storage container, it is in contact with the silicon crystal when the temperature is lowered from 1414 ° C. to 24 ° C. The amount of heat shrinkage on the inner surface is Δl = 0.0765 mm according to the following equation (2).

  That is, the amount of heat shrinkage of the inner diameter of the quartz glass melt storage container is almost an order of magnitude smaller than the amount of heat shrinkage of the silicon crystal, and the difference between them is ΔL−Δl = 0.695 [mm] −0.0765 [mm]. = 0.62 [mm]. This is a value in diameter, and there is a difference of 0.62 [mm] ÷ 2 = 0.31 [mm] per radius between the inner diameter side of the quartz glass melt storage container and the outer diameter side of the silicon crystal body. There will be a gap in the gap.

On the other hand, when the cylindrical silicon crystal body having an inner diameter of 80 mm falls from 1414 ° C. to 24 ° C., the thermal shrinkage amount is ΔR = 0.556 [mm] according to the following equation (3).

Here, when magnesia having a thermal expansion coefficient of 12 × 10 ⁻⁶ [/ ° C.] is used as the core, the core is in contact with the inner surface of the cylindrical silicon crystal body when the temperature is lowered from 1414 ° C. to 24 ° C. The amount of heat shrinkage on the outer surface is Δr = 1.334 [mm] according to the following equation (4).

  From the above formulas (3) and (4), the thermal shrinkage difference between the cylindrical silicon crystal inner diameter and the core outer diameter is ΔR−Δr = 1.334 [mm] −0.556 [mm] = 0.778. [Mm]. This is a value in diameter, and a difference of 0.778 [mm] ÷ 2 = 0.389 [mm] per radius occurs between the inner diameter side of the silicon crystal and the outer diameter side of the magnesia core, that is, there is a gap between the two. become.

  As described above, when the cylindrical silicon crystal is manufactured, the silicon crystal, the melt storage container, and the core are appropriately selected by taking into consideration the values of the thermal expansion coefficients of each other, so that the crystal becomes room temperature. In addition, there is a gap between the silicon crystal body and the liquid storage container and between the silicon crystal body and the core, and the silicon crystal body is separated and obtained.

  In addition, since the meltability of the silicon melt is maintained, the solidified silicon crystal does not adhere to the melt storage container or the core, and is not damaged due to the difference in thermal expansion coefficient. In the silicon crystal produced in this way, a hollow portion is formed by the core. Accordingly, it is possible to produce a cylindrical silicon crystal from a silicon raw material without performing a cutting process.

  In addition, by making the purity of silicon nitride applied to the inner surface of the melt storage container and the outer surface of the core higher than the purity of the core material, the contamination of the silicon melt with impurities is suppressed, The quality of the produced cylindrical silicon crystal can be improved.

  Furthermore, the depth of the hollow portion of the cylindrical silicon crystal can be changed by adjusting the holding state of the core. That is, when the bottom surface of the core is brought into close contact with the bottom surface of the melt storage container, the hollow part of the produced cylindrical silicon crystal is opened at both bottom surfaces, and the bottom surface of the core is the bottom surface of the melt storage container. The cylindrical silicon crystal to be manufactured becomes a bottomed cylindrical shape by being held in a state of being separated from the bottom. Then, by adjusting the distance between the bottom surface of the core and the bottom surface of the melt storage container, the depth and bottom thickness of the hollow portion of the produced cylindrical silicon crystal can be changed.

  The bottomed cylindrical crystal according to the present invention is manufactured by the cylindrical silicon crystal manufacturing method according to the present invention, and a material suitable for a focus ring can be obtained by cutting perpendicularly to the longitudinal direction. In addition, since it has a bottom wall, it can be used as a container as required.

It is sectional drawing which shows the outline of the casting_mold | template used for the Example of the cylindrical silicon crystal manufacturing method which concerns on this invention. It is a perspective view which cut | disconnects and shows the cylindrical silicon crystal body manufactured in the Example. It is sectional drawing which shows the casting_mold | template with the state which kept the bottom face of the core away from the bottom face of the beneficial storage container. It is a perspective view which cuts the one part and shows the cylindrical silicon crystal manufactured when the bottom face of a core is kept away from the bottom face of a beneficial storage container.

With reference to FIG. 1 and FIG. 2, an embodiment of a method for producing a cylindrical silicon crystal according to the present invention will be described.
First, the casting_mold | template 1 used with the manufacturing method which concerns on an Example is demonstrated. As shown in FIG. 1, a mold 1 includes a carbon container 2, a melt storage container 3 installed inside the carbon container 2, and a core 4 arranged in an arbitrary state inside the melt storage container 3. And a lid 5 that opens and closes the upper openings of the carbon container 2 and the melt storage container 3. The melt storage container 3 is made of quartz having a smaller thermal expansion coefficient than that of the silicon crystal, and the core 4 is made of alumina, which is a material having a higher thermal expansion coefficient and higher melting point than that of the silicon crystal. . The carbon container 2 employs a known susceptor used to support a known quartz crucible, and the lid 5 is formed of the same material (carbon) as the carbon container 2. . The mold 1 is housed in a vacuum chamber (not shown), and heaters (not shown) are installed above and below the mold 1.

Next, a method for producing a cylindrical silicon crystal using this mold 1 will be described. In manufacturing the crystal body, first, silicon nitride (Si ₃ N ₄ ) is applied to the inner surface of the melt storage container 3 and the outer surface of the core 4 to maintain the liquid-liquid property of the silicon melt in the vacuum chamber. Environment. In order to prepare such an environment, while heating the inside of the vacuum chamber, a vacuum state of 10 ⁻⁴ Torr or less is obtained by roughing the vacuum to remove impurities such as moisture and oxygen that hinder the liquid-melting property of the silicon melt. After the vacuum heat treatment is sufficiently performed, it is possible to maintain the liquid-melting property of the silicon melt by introducing and flowing argon gas into the vacuum chamber.

  After preparing the environment in the vacuum chamber, the silicon melt 6 is formed by the inner surface of the melt storage container 3 and the outer surface of the core 4 by melting the high-purity silicon raw material previously charged in the melt storage container 3. Fill the void.

  When the filling of the silicon melt 6 is completed, the output of the heaters arranged above and below the mold 1 is gradually weakened, and a temperature gradient is provided from the bottom side of the melt storage container 3 to the upper side to melt the silicon melt 6. The liquid storage container 3 is solidified from the bottom side. At this time, the argon liquid is always allowed to flow into the vacuum chamber, so that the liquid-cooling property of the silicon melt 6 is maintained.

  After the silicon melt 6 is solidified, the silicon crystal formed inside the melt storage container 3 contracts from the melt storage container 3 having a small thermal expansion coefficient and is separated from the melt storage container 3. Become. Further, the core 4 having a thermal expansion coefficient larger than that of the silicon melt 6 contracts more than the silicon crystal, so that it is separated from the silicon crystal formed on the outside thereof. In addition, since the liquid crystallinity of the silicon melt 6 is maintained, the solidified silicon crystal is not fixed to the melt storage container 3 and the core 4 and is not damaged due to the difference in thermal expansion coefficient.

  When the crystal body is formed, the mold 1 is taken out from the vacuum chamber, and the silicon crystal body is taken out from the mold 1. As shown in FIG. 2, a hollow portion 7 a is formed by the core 4 in the formed silicon crystal body 7. That is, a cylindrical silicon crystal is manufactured from a silicon raw material without cutting.

  When the above manufacturing method was carried out using the mold 1 shown in FIG. 1, a cylindrical silicon crystal having an outer diameter of 80 mm and a height of 50 mm and having a hollow part with a diameter of 60 mm and made of columnar crystal silicon is obtained. I was able to. The purity of the cylindrical silicon crystal manufactured by the above manufacturing method is affected by the purity of silicon nitride applied to the inner surface of the melt storage container 3. It was confirmed in this example that the purity was higher than the purity of the material, which was comparable to a commercially available columnar silicon crystal.

As long as the core 4 has a coefficient of thermal expansion larger than that of silicon (5 × 10 ⁻⁶ [/ ° C.]), the material can be selected as appropriate, and the alumina (thermal expansion coefficient 8 × 10 ⁻⁶ [/ ° C.) can be selected. ]), Silicon carbide (thermal expansion coefficient 6 × 10 ⁻⁶ [/ ° C.]) or magnesia (thermal expansion coefficient 12 × 10 ⁻⁶ [/ ° C.]) may be used.

  Moreover, in the casting_mold | template 1 shown in FIG. 1, the bottom face of the core 4 is closely_contact | adhered to the bottom face of the melt storage container 3, and the hollow part 7a of the cylindrical silicon crystal body 7 manufactured is opened on both bottom faces. However, the core 4 may be held in a state where the bottom surface of the core 4 is separated from the bottom surface of the melt storage container 3. FIG. 3 shows a state where the core 4 is held in a state where the bottom surface of the core 4 is separated from the bottom surface of the melt storage container 3. In this case, as shown in FIG. 4, the cylindrical silicon crystal 8 to be manufactured has a bottomed cylindrical shape having a bottom wall 8a. In addition, you may change the depth of the hollow part of the cylindrical silicon crystal manufactured, and the thickness of the bottom by adjusting the distance of the bottom face of the core 4 and the bottom face of the melt storage container 3. FIG.

  The bottomed cylindrical silicon crystal body 8 can obtain a material suitable for a focus ring by cutting perpendicularly to the longitudinal direction, and has a bottom wall 8a. It can also be used.

DESCRIPTION OF SYMBOLS 1 Mold 2 Carbon container 3 Melt storage container 4 Core 5 Lid body 6 Silicon melt 7 Cylindrical silicon crystal body 7a Hollow part 8 Bottomed cylindrical silicon crystal body 8a Bottom wall

Claims (4)

Using a melt storage container formed of a material having a smaller thermal expansion coefficient than the silicon crystal and a high melting point, and a core formed of a material having a larger thermal expansion coefficient than the silicon crystal and a high melting point, Silicon nitride (Si ₃ N ₄ ) is applied to the inner surface of the melt storage container and the outer surface of the core, the core is placed inside the melt storage container, and the inner surface of the melt storage container and the A silicon melt is filled into a gap formed between the outer surface of the core and a temperature gradient is provided from the bottom side to the upper side of the melt storage container while maintaining the liquid-liquidity of the silicon melt. A method for producing a cylindrical silicon crystal, comprising solidifying a liquid. The material of the melt storage container is quartz or carbon having a smaller thermal expansion coefficient than that of the silicon crystal, and the material of the core is any of silicon carbide (SiC), alumina (Al ₂ O ₃ ), or magnesia (MgO). The cylindrical silicon crystal manufacturing method according to claim 1.   The cylindrical silicon crystal production according to claim 1 or 2, wherein the purity of silicon nitride applied to the inner surface of the melt storage container and the outer surface of the core is higher than the purity of the material of the core. Method.   The cylindrical silicon crystal manufacturing method according to claim 1, wherein the core is held in a state in which a bottom surface of the core is separated from a bottom surface of the melt storage container.

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